The present invention relates to a keyboard and, more particularly, to a keyboard constituted, when transmitting data obtained by a keyboard operation to a host signal processor, to minimize power consumption in the keyboard.
Generally, a keyboard is used as connected to a signal processor such as a personal computer by cable and has a key matrix with many keys laid out, an input/output circuit for performing input/output operations with the key matrix, a controller for controlling the entire operation of the keyboard, a clock signal generator for forming a clock signal for obtaining a scan signal, a display device for indicating a key-operated state and so on, an interface circuit for providing interface between the keyboard and the signal processor, and a built-in power supply.
FIG. 4 shows a block diagram illustrating an example of the constitution of a known keyboard.
Referring to FIG. 4, a keyboard 40 comprises a key matrix 41 with many keys laid out, an input/output (I/O) circuit 42 for receiving data associated with key operations from the key matrix 41, a controller (CPU) 43 for controlling the entire operation of the keyboard 40, an interface (I/F) circuit 44 for providing interface between the keyboard 40 and the signal processor (not shown) such as a personal computer, an clock signal generator 45 for forming a clock signal for obtaining a signal for scanning the key matrix 41, a ROM 46 for storing a program for operating the controller 43, a RAM 47 for use in the data processing by the controller 43, and display device (IND) for indicating a key-operated state and so on, a cable 49 for connecting the interface circuit 44 to the signal processor, and a built-in power supply 50.
In the above-mentioned constitution, the controller 43 performs various operations as follows. First, the controller 43 generates a scan signal for scanning horizontally and vertically the keys arranged on the keyboard sequentially. Second, the controller 43 receives switch data corresponding to an operated key when the keys have been scanned. Third, the controller 43 converts the received switch data to a key code (or a keyboard code) to be transmitted to the signal processor. Fourth, the controller 43 transmits the switch code to the signal processor via the interface circuit 44 and the cable 49. Fifth, the controller 43 transmits required display data to the display device 48. Sixth, the controller 43 executes required signal processing in response to command data supplied from the signal processor via the cable 49.
The keyboard 40 having the above-mentioned constitution operates as follows in general.
When any of the keys arranged on the key matrix 41 is operated, the controller 43 sequentially receives the switch data corresponding to the operated keys via the input/output circuit 42. Then, the controller 43, based on the operating program stored in the ROM 46, converts the switch data to key codes by use of the RAM 47 and transmits sequentially the obtained key codes to the signal processor via the interface circuit 44 and the cable 49. If, during or immediately before or after this transmission, some command data are supplied from the signal processor to the controller 43, the controller 43 performs a control operation corresponding to that command data.
In the above-mentioned known keyboard 40, when the signal processor is in the active state, the scan signal is always supplied from the controller 43 to the key matrix 41 via the input/output circuit 42 for performing key scan on the keys arranged on the key matrix 41.
Also, in the above-mentioned known keyboard 40, every time any of the keys on the key matrix 41 are operated, the controller 43 generates key codes corresponding to the operated keys and transmits the generated key codes to the signal processor via the interface circuit 44 and the cable 49. Especially, when a single key is operated repeatedly, the controller 43 generates a corresponding key code repeatedly during the continuous operation and transmits the repeatedly generated key code to the signal processor without drop.
Thus, in the known keyboard 40, the controller 43 is always operating. This increases the availability of the controller 43, thereby posing a problem of increased power consumption of the controller 43. Especially, this problem becomes conspicuous when the keyboard is driven by the build-in battery 50.